The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Complex signals can be represented in a time and/or a frequency domain. Signals may be transformed from the time domain to the frequency domain and vice versa. Transformation from the time domain to the frequency domain may be implemented by a Fourier transform. The Fourier transform provides a spectrum of frequency components (i.e., spectra), referred to as “harmonics,” each of which has a corresponding magnitude. Considered together, the signal spectra constitute a frequency domain representation of a given signal.
One notable use of such a transformation, is to electronically determine the fly height of a read/write head in a hard disk drive (HDD). The fly height is the height of the head relative to a recording medium.
Methods for detecting fly height generally employ detecting a known pattern written on the storage medium. In response to detecting the pattern, the head produces a signal. A ratio in harmonic magnitude of the fundamental frequency (i.e. first harmonic (Fc)) and corresponding third harmonic (3Fc) of the signal may directly correlate to a change in fly height (ΔD) of the head. This relationship may be expressed as:ΔD=|3Fc|÷|Fc|
In storage media systems, fly height of the head is often maintained within a prescribed region. If the fly height is too great, the signals transmitted and read by the head may be too weak for accurate data storage and retrieval. If the fly height is too small, the head may physically contact the medium, causing damage to the medium and/or loss of the data stored on the medium.